It is well known that an imbalance in current rates of energy production and consumption could lead to an impending national energy crisis of severe proportions, bringing about serious shortages and higher prices of fuels, including those conventionally used for heating lumber dry kilns. A readily available supply of wood fiber material of low commercial value has forced lumber producers to seek a satisfactory manner of utilizing normally wasted wood fiber as a means of producing heat for the drying of green lumber. Methods now available require at economically prohibitive expense preparation of the wood fiber prior to burning, where expensive equipment of high capital construction cost, particularly the high horsepower electrical motors necessary, offsetting much of the savings possible from use of waste wood fiber as a fuel for heating lumber dry kilns. Moreover, methods now available produce residue deposit on lumber, such deposits presenting quality control problems, as well as unpleasant and unhealthful conditions for personnel charged with final machining of kiln dried lumber. Such methods also produce a pollution hazard with respect to atmospheric emission of pollutants. In addition, known methods present mechanical problems which produce prohibitive maintenance expense and loss of production time.
Previous examples of equipment for destroying cellulosic materials are known, including U.S. Pat. No. 3,886,873, issued June 3, 1975 to Sundqvist et al showing a method of destroying waste by gasification and subsequent combustion of the gaseous products, but using a rotary grate with a separate fan for introduction of combustion air. U.S. Pat. No. 2,165,802, issued July 11, 1939 to Longtin, discloses a sawdust burning furnace with a horizontal grate having parallel slots, and the Doherty patent (U.S. Pat. No. 1,154,910), patented Sept. 28, 1915, shows a furnace with an inclined grate on which kindling is ignited, but the grate so described fails to withstand the temperatures and abrasion which results from normal use. U.S. Pat. No. 3,831,535 issued Aug. 27, 1974 to Baardson discloses a burner system in which waste wood is burned as a source of heat while reducing the volume of pollutant fumes. However, it is necessary in the Baardson system to grind up raw waste wood to a fine powdery form for introduction into a combustion chamber. Caughey in U.S. Pat. No. 4,030,895, issued June 21, 1977, shows apparatus for generating combustible fuel gases having an inclined grate dividing the chamber into two parts.
Other patents showing generally the carbonizing, gasification, destruction, or firing of various cellulosic materials include the following:
______________________________________ 3,398,058 Campbell Aug. 20, 1968 3,865,053 Kolze Feb. 11, 1975 3,746,521 Giddings July 17, 1973 3,729,298 Anderson April 24, 1973 2,086,033 Huttner July 6, 1937 2,071,678 Bellay Feb. 23, 1937 1,917,196 Perry July 4, 1933 353,966 Rathbun Dec. 7, 1886 ______________________________________
A drawback associated with each of the patents listed above is their failure to teach a grating or support material which is durable in extended use. Refractory materials have been manufactured from a variety of components, including metals in particulate form. U.S. Pat. No. 2,881,083, patented Apr. 7, 1959 by Veale discloses addition of iron powder to a kaolin-type clay, in order to produce a refractory brick composition. U.S. Pat. No. 3,382,082 to Eubanks et al, patented May 7, 1968, teaches introduction of a metal powder into a ceramic refractory composition, and U.S. Pat. No. 220,715, issued Oct. 21, 1879 to Kinklein, discloses addition of iron filings to clay to produce a fire clay which makes tight stove joints. Disclosure of incorporation of aluminum metal in refractory composition can be found in U.S. Pat. No. 3,649,315, issued Mar. 14, 1972 to Booth, and in U.S. Pat. No. 2,613,153, patented Oct. 7, 1952 by Stafford, with the latter patent mentioning kaolin specifically.